1. Field of the Invention
The invention relates to a covering for an architectural opening, such as a roller shade for a window, having one or more, vertically-extending parallel layers of shade material. This invention especially relates to a roller shade, to which front and rear layers of a shade material are attached, so that the layers can be moved parallel to one another to open and close the shade to light.
2. Description of the Relevant Art
Architectural coverings are known with two vertically-extending parallel sheet layers, which are disposed one in front of the other and each of which has an array of elongated, longitudinally-extending, vertically-alternating transparent and opaque stripes. When the transparent stripes of one layer have been in vertical alignment with the transparent stripes of the other layer, light has been transmitted through the coverings, but when the opaque stripes of one layer have been vertically aligned with the transparent stripes of the other layer, these coverings have blocked light. See GB 926 663, GB 1 227 619, U.S. Pat. No. 2,029,675, FR 1 366 224, DE 2 326 438, NL 7209084 and U.S. Pat. No. 6,189,592.
The two vertically-extending layers of such coverings have been made of fabric, plastic or the like and have been connected at their top and/or bottom ends by top and/or bottom bars. A special fabric, very suitable for such coverings, has been described in EP 1 088 920 and EP 1 241 318. This fabric is a two layer woven fabric having one or more binder threads connecting the layers, so that one layer could slide along the binder threads and along the other layer.
Such double layer architectural coverings have been made as roller shades, having a roller to which the layers of shade materials have been attached at radially different locations of the roller, so that partial rotation of the roller has displaced the layers relative to each other and continued rotation has wound the layers about the roller. The layers of shade materials of roller shades have generally been attached to their rollers by folding each layer over an attachment member or rod and then sliding or pushing the attachment member with the layer folded over it into a groove or slit of the roller. See GB 19 449 and DE 25 19 365.
However, the use of an attachment member has proven unsatisfactory for attaching a layer of a shade material to a roller. If the shade material has not been well aligned with the roller when folded over its attachment member, the shade has not hung straight down from the roller and has not operated well. Also, the layer folded over the attachment member has sometimes tended to get out of alignment during assembly of the roller shade which has been hard to correct afterwards. With two layer roller shades, it has been particularly difficult to align the complementary patterns, typically stripes of the front and rear layers, using such attachment members. Also, the layers have tended to become skewed, relative to one another, when wound about the roller if both layers have not been perfectly aligned with the roller. When the layers have not been perfectly aligned, light has shone through gaps between the stripes, and the patterns have no longer appeared to be complimentary.